ruby-on-rails - 检测现有 ActiveRecord 关联的更改

Question

我正在编写一个 ActiveRecord 扩展，它需要知道何时修改关联。我知道通常我可以使用 :after_add 和 :after_remove 回调，但是如果关联已经声明了怎么办？

Answer 1

您可以简单地覆盖关联的设置器。这也将让您更自由地了解更改，例如在更改之前和之后拥有 assoc 对象。

class User < ActiveRecord::Base
  has_many :articles

  def articles= new_array
    old_array = self.articles
    super new_array
    # here you also could compare both arrays to find out about what changed
    # e.g. old_array - new_array would yield articles which have been removed
    #   or new_array - old_array would give you the articles added 
  end
end

这也适用于批量分配。

Answer 2

正如您所说，您可以使用after_add和after_remove回调。另外after_commit为关联模型设置过滤器并通知“父”有关更改。

class User < ActiveRecord::Base
  has_many :articles, :after_add => :read, :after_remove => :read     

  def read(article)
    # ;-)
  end
end 

class Article < ActiveRecord::Base
  belongs_to :user

  after_commit { user.read(self) }
end